Volume 3 of Advances in Developmental Biology and Biochemistry consists of five chapters that review specific aspects of mammalian and fly development. In Chapter 1, D. Chapman and D. Wolgemuth discuss the role of protein kinases, especially tyrosine-and serine/threonine kinases, in regulating cell cycle events during mammalian gametogenesis. IN Chapter 2, M. Lundell and J. Hirsh discuss the regulation of the DOPA decarboxylase gene during Drosophila development. DO PA decarboxylase is a key enzyme in biogenic amine biosynthesis and its expression is subject to both transcriptional and post-transcriptional regulation. In Chapter 3, S. Potter discusses the role of homeobox genes as master switches determining the developmental destinies of groups of cells during murine development. In Chapter 4, G. Cooper discusses the expression and function of the c-mos proto-oncogene in mammalian germ cells where it plays a central role in regulating the meiotic cell cycle. In Chapter 5, F. Beermann, R. Gan?, and G. Sch?tz discuss the regulation of pigmentation during mammalian development, with emphasis on the production of melanin in mouse melanocytes.